1. Introduction
The pre-mining gas control model in Baode Coal Mine’s large-panel working face requires that inseam directional drilling borehole can reach more than 3 000m. The existing technical equipment still have problems such as large water pressure consumption, limited transmission distance of wired measurement while drilling signals, and inability to recycle the drill fluid, which restricted the development of directional drilling along the coal seam.
2. Treatment solution
Sliding drilling drag reduction technology based on downhole motor hydraulic pressure and super long drilling tool forward and reverse torsion feed, and composite drilling trajectory control technology based on rotary drilling inclination angle control were developed. A low-pressure water consumption water inlet system, a mud pulse wireless measurement while drilling system and a flushing fluid purification circulation system were also designed. In accordance with the production needs of Baode Coal Mine, the construction of ultra-long through directional holes along the coal seam was carried out.
3. Construction situation
At No. 1 intake alley, section 27, Pentan district, Baode County Coal Mine, the directional drilling was carried out, adopting ZDY15000LD directional drilling equipment, YHD3-3000 type mud pulse wireless measurement while drilling system, high-strength non-cable directional drilling tool independently innovated by CCTEG Xi’an Research Institute. The drilling operation cost 21 days, to achieve a borehole depth of 3353m. Total drilling footage is 4428m with 120mm diameter. Borehole sidetracks reached roof and floor for 13 times. The error of target coordinate of drilling through the tunnel is less than 0.15%. At present, average daily gas extraction of the borehole is more than 5000m3.
4. Achieved accomplishment
The borehole broke inseam directional drilling depth record that created by CCTEG Xi ’an Research Institute in early 2019. It realized stable signal transmission of mud pulse wireless measurement while drilling (MWD) over 3000m deep and ultra-long distance high precision target hitting.
Industrial application of the newly developed flushing fluid purification circulation system for underground coal mines has solved the problem of large water consumption and large sewage discharge in the construction of ultra-long boreholes, and realized directional drilling flushing fluid to be transferred from "open" to "closed" cycle. The successful implementation of the 3353 m ultra-long inseam directional borehole drilling is a new milestone in the development of downhole motor directional drilling technology and equipment, indicates that we have reached the international leading level in this field. It is of great significance to promote the advancement of gas control in large areas of coal seams, the prevention of water hazards, and geological exploration.
5. FAQ
Q1: What technologies are used to realize ultra-long directional drilling along coal seam?
A: We have adopted the drag reduction technology of downhole motor hydraulic pressure and reverse twist feed of super-long drilling tools, as well as the control technology of dip angle of rotary drilling and the control technology of compound drilling trajectory of sidetracking branch. Low pressure water inlet system, mud pulse wireless measurement while drilling system and flushing liquid purification circulation system are also designed to realize the super-long inseam directional drilling.
Q2: What can your company do in this area?
A: We can solve the main gas drainage problems encountered in the process of mine exploration, construction, production and shut-down.
Q3: What advantages does your company have over other companies?
A: We are committed to the design and construction of coal seam gas control, and can supply comprehensive service of coal seam gas control technology and equipment.
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